Coracoacromial Ligament

The coracoacromial ligament is a strong triangular band of fibrous tissue that connects the coracoid process to the acromion of the scapula. Although it does not directly cross or stabilize a joint, it plays an important role in forming the coracoacromial arch, a protective structure overlying the head of the humerus. This arch prevents superior displacement of the humeral head and contributes to shoulder joint stability.

Location

The coracoacromial ligament is located on the superior aspect of the shoulder, forming a bridge between two bony processes of the scapula. It lies anterior to the supraspinatus tendon and subacromial bursa, deep to the deltoid muscle.

Structure

• Flat, triangular band of dense connective tissue.
• Runs obliquely laterally and posteriorly from the lateral edge of the coracoid to the undersurface of the acromion.
• Fibers are oriented to resist downward displacement and superior humeral translation.
• Forms the roof of the subacromial space.

Function

• Superior shoulder protection: Forms a protective vault over the head of the humerus, preventing upward dislocation.
• Stabilization aid: Assists in maintaining shoulder alignment during lifting or pushing movements.
• Attachment point: Provides a structural barrier to prevent impingement of deeper structures.

Physiological Role(s)

• Prevents superior escape of the humeral head, especially when rotator cuff function is impaired.
• Acts as a passive restraint, particularly when the arm is abducted or elevated.
• Supports the subacromial space, minimizing compression of the bursa and supraspinatus tendon.

Relations

• Superiorly: Deltoid muscle and subcutaneous tissue of the shoulder.
• Inferiorly: Subacromial bursa and supraspinatus tendon.
• Anteriorly: Clavicle and coracoclavicular ligaments.
• Posteriorly: Acromion and posterior deltoid.

Coracoacromial Arch

The coracoacromial ligament, along with the acromion, coracoid process, and inferior surface of the acromioclavicular joint, forms the coracoacromial arch. This arch acts as a functional roof over the glenohumeral joint and plays a key role in preventing superior dislocation of the humeral head.

Development

The coracoacromial ligament forms from connective tissue condensations in the developing shoulder region. It is derived from the same mesenchymal tissues that form the joint capsule and surrounding ligaments. By birth, the ligament is well-formed and continues to mature with mechanical use and muscular activity in early life.

Clinical Significance

• Shoulder impingement syndrome: Thickening or calcification of the coracoacromial ligament may reduce subacromial space, compressing the supraspinatus tendon or bursa and causing pain.
• Rotator cuff pathology: The ligament may contribute to friction or impingement of the rotator cuff, especially in overhead activities.
• Coracoacromial ligament release: In cases of chronic impingement, surgical release or resection of the ligament may be performed during subacromial decompression.
• Fracture support: Even when the clavicle or acromion is fractured, the intact coracoacromial arch may help prevent superior humeral dislocation.

Imaging

• Ultrasound: May detect thickening or calcific changes in the ligament in impingement syndromes.
• MRI: Useful for assessing subacromial space and visualizing the ligament in relation to rotator cuff tendons and bursa.
• X-ray: Cannot directly visualize the ligament, but may show secondary signs of impingement or acromial spurs.

Anatomical Variations

• Thickness and length of the ligament may vary significantly between individuals.
• In some people, the ligament is bifid or trilaminar, with multiple fiber layers.
• Calcification of the ligament is more common with aging and may be associated with chronic shoulder pathology.